As is known, the working processes commonly used in industrial plants such as iron and steel works, refineries, waste-to-energy plants and the like produce fumes which contain toxic, pathogenic and/or polluting agents such as particulate matter, dioxins, furans, polychlorobiphenyls, chlorophenoxy compounds, nitrogen oxides or dioxides, sulphur dioxide, etc.
In general, particulate matter, anhydrides and nitrogen monoxides and dioxides are irritants for the respiratory systems, causing in human beings respiratory illnesses and diseases such as asthma, bronchitis and infections of the respiratory tracts. Moreover, particulate matter, in particular ultrafine dust particles, may convey pollutants also into the pulmonary alveoli.
The systems for filtering fumes which are currently known consist for example of electrofilters, bag filters, cyclone dust separators, hydraulic dust separators, active carbons, etc.
These systems, however, have a series of drawbacks. For example, they require frequent periodic maintenance and therefore have high maintenance costs. Moreover, they are subject to malfunctions due to the significant pressure losses.
Furthermore, the known systems have not insignificant limitations of a physical and mechanical nature. For example, bag filters perform filtering by means of micro-perforated bags capable of retaining dust particles with a diameter greater than that of the holes. However, these filters allow dust particles with a diameter smaller than that of the holes to pass through. If the diameter of the holes were too small, there would be problems with the air flow. Therefore, these filters are not suitable for retaining in an efficient manner ultrafine dust particles, with a diameter of less than 5 microns.
Many of these systems are also not compatible with high temperatures, are adversely affected by the presence of moisture (bag filters) and sometimes have a very limited efficiency as regards filtering of particulate matter (conventional cyclones). Almost always they consist of systems which have exclusively a very limited dedusting capacity for fumes (are ineffective for eliminating ultrafine particles with a diameter of less than 5 μm) and are unsuitable for removal of the pollutants except where costly plasma thermal destruction systems are used with subsequent washing and drying of the fumes.
Examples of known systems such as those described are contained in the publications KR20020044845, WO2009087100, WO8800610A1 and WO0006289.
Other systems are also known from the documents US2014/238239, DE102004039182, FR1024439, WO2009155974, US2008250933 and U.S. Pat. No. 3,348,830. These systems are substantially conventional cyclones, namely they have a form extending spirally around an axis of extension along which the fumes flow. The fumes, travelling along the cyclone, are subject to centrifugal forces which push the solid particles contained therein towards the outer walls of said cyclone. Moreover, the configurations of the ducts in these systems do not have the necessary characteristics for creating vacuum effects useful for removal of the particulate matter.
When the particles strike the walls they are separated from the stream of fumes and collected. These systems have the drawbacks described above. Moreover, as already mentioned, they are unsuitable for the removal of fine dust particles with a diameter of less than 10 μm (microns).